1. Field of the Invention
The present invention relates to a noncontacting card which transfers electric power and signals by electromagnetic coupling, a terminal for it, and furthermore noncontacting transmission systems.
2. Description of the Related Art
FIG. 17 shows an example of a conventional noncontacting card, which is disclosed in U.S. Pat. No. 4,791,285. This noncontacting card 1 contains an electric circuit 3 and four coils 4 to 7 connected to this electric circuit 3. The coil 4 is used for receiving electric power from a terminal not shown in this figure. The coil 5 is used for transmitting data to a terminal. The coil 6 is used for receiving data from a terminal and the coil 7 is used for receiving a mode setting signal from a terminal. Taking the coil 4 as an example, details are shown in FIG. 18. The coil 4 has a spiral shape with a single wire on a printed circuit board 2. An end of the coil 4 is connected to the circuit 3 via a wire on a surface of the printed circuit board 2, and the other end is connected to the circuit 3 via a wire on the back surface of the printed circuit board. 2.
A coil holder of a terminal is shown in FIG. 19. This coil holder 8 has an upper board 9, a vertical board 12, and a lower board 13, and has a U-like shape. Spiral coils 11a and 11b are located on the upper board 9 and the lower board 13 respectively. One end of each of spiral coils 11a and 11b is connected to electrodes 10 and 14, respectively. These spiral coils 11a and 11b are also connected to each other in series via a wire on the vertical board 12. Only a pair of coils are shown in FIG. 19, but the coil holder 8 has four pairs of coils corresponding to each of the coils 4 to 7 on the noncontacting card 1.
The operation of the coils 11a and 11b shown in FIG. 19 is explained next, assuming that these coils are used for transmitting electric power, i.e. correspond to the coil 4 on the noncontacting card 1. When a noncontacting card 1 is inserted into the coil holder 8 so that the center axis of the coil 4 on the noncontacting card 1 coincides with the center axes of the coils 11a and 11b of the coil holder 8, and furthermore AC current is supplied from a terminal via electrodes 10 and 14, an AC voltage is induced at the coil 4 on the noncontacting card 1 by the electromagnetic coupling. In this case, because coils 11a and 11b of a coil holder 8 are connected in series so that both coils generate magnetic flux in the same direction, the generated AC electromagnetic force is twice as strong as if just one coil, either 11a or 11b, is used.
However, transmission efficiency is low, because conventional noncontacting cards transmit electric power and data with a single wire spiral coil. As a result of this, a terminal cannot transmit strong enough electric power. Moreover, when a large gap exists between coils of a noncontacting card and a terminal, accurate transmission is impossible and a noncontacting card does not function well.
When, as shown in FIG. 19, two coils connected in series are used to improve transmission efficiency, the electric resistance and inductance of the coils become large due to the wiring length of coils. Therefore, the power loss becomes large bringing about difficulties in transmission of electric power and data using high frequency carriers such as higher than 1 MHz.